Field of the Invention
The invention pertains to the field of electric variable cam timing actuators or “phasers” (e-phasers). More particularly, the invention pertains to an electric phaser with an anti-backlash planetary drive.
Description of Related Art
A variable cam timing (VCT) system measures the angular displacement, or phase angle, of a camshaft, relative to the crankshaft to which it is operatively connected and then alters the phase angle to adjust various engine characteristics in response to demands for either an increase or a reduction in power. Typically, there is a feedback loop in which the desired values of such engine characteristics are measured against their existing values, and changes are effected inside the engine in response to any variances. To accomplish this, modern automobiles usually have one or more Electronic Control Units (ECU), which constantly analyze data fed into them from various parts of the engine or from other parts of the automobile, such as, for example, exhaust gas sensors, pressure sensors, and temperature sensors. A control signal is then emitted in response to such data. For example, with regard to VCT systems, as changes occur in engine or external conditions, the angular displacement between the camshaft and the crankshaft is adjusted accordingly.
A VCT system includes a cam phasing control device, sometimes referred to as a phaser, control valves, control valve actuators, and control circuitry. VCT is a process that refers to controlling and varying, when desirable, the angular relationship (the “phase”) between the drive shaft and one or more camshafts, which control the engine's intake and exhaust valves. The current state of the art for automotive camshaft phasers is either an Oil Pressure Actuated (OPA) cam phaser or a Cam Torque Actuated (CTA) cam phaser, with the later having some advanced features, such as fast operation with low oil pressure and a mid-position lock feature.
Many automotive companies are now working on electric phasers (e-phasers) for camshafts to improve the actuation rate and range of authority and operation either before engine start or during engine cranking. An e-phaser is driven by an electric motor to control and vary the angular relationship between the drive shaft and one or more camshafts. In response to input signals, the electric phaser adjusts the camshaft to either advance or retard engine timing.
These systems have a high ratio gear train to phase the camshaft relative to the crankshaft by means of a motor spinning at cam speed. When the motor spins faster than the camshaft, the phaser phases the camshaft relative to the crankshaft in one direction, and as the motor slows down, the cam-to-crank phase moves in the opposite direction. These high ratio gear trains include cycloidal-style gear trains, harmonic gear trains, or some other type of high ratio epicyclical gear trains.
U.S. Pat. No. 7,261,667, entitled “System and Method for Reducing Backlash in a Planetary Gear Set” and issued Aug. 28, 2007 to Berger, discloses a planetary gear set with a planet carrier including a first part that supports at least one forward-torque carrying planet gear that has at least one tooth contacting a drive side of gear teeth of an associated sun gear and ring gear and a second part that supports at least one reverse-torque carrying gear that has at least one tooth contacting a coast side of gear teeth of the associated sun gear and ring gear. The second part of the carrier is rotationally biased relative to the first part to reduce or eliminate effective backlash of the gear set.
U.S. Pat. No. 8,313,411, entitled “Backlash-free Planetary Gear Unit with Split Planet Gears, which are Preloaded by Spring Bars Arranged Parallel to the Planetary Axis of Rotation” and issued Nov. 20, 2012 to Schafer, discloses a planetary gear unit including a sun gear, an internal gear, and at least one planet gear in mesh with the sun gear and the internal gear. The planet gear is arranged on a planet carrier such that it is rotatable about a planetary axis of rotation. The toothed planet gear has a plane of division oriented perpendicular to the planetary axis of rotation, by means of which the planet gear is divided into a first planet subgear and a second planet subgear. The first planet subgear is preloaded relative to the second planet subgear by a spring bar arranged in these two planet subgears substantially parallel to the planetary axis of rotation. A plurality of spring bars is arranged around the planetary axis of rotation.
WO 2014/092963, by Showalter, entitled “Split Ring Gear Planetary Cam Phaser” and published Jun. 19, 2014, discloses a cam phaser for dynamically adjusting a rotational relationship of a camshaft of an internal combustion engine with respect to an engine crankshaft. The cam phaser can include a planetary gear system having a split ring gear, including a sprocket ring gear to be driven by the engine crankshaft through an endless loop power transmission member and a camshaft ring gear connectable for rotation with the camshaft. A sun gear can be located concentric with the split ring gear, and a number of planet gears can be in meshing engagement between the sun gear and the split ring gear. The camshaft ring gear can have a different number of teeth, greater or lesser, than the sprocket ring gear by a value corresponding to a multiple of the number of planet gears to provide tooth alignment at an engagement position of each of the planet gears.
The above-mentioned references are hereby incorporated by reference herein.